The fluid dynamic bearing device supports a shaft member by fluid film formed in a bearing gap so as to be capable of relative rotation. The bearing device of this type is excellent particularly in rotational accuracy at the time of high-speed rotation, silence, and the like, and is suitably used as a bearing device for a motor mounted to various electrical apparatuses such as an information apparatus. Specifically, the bearing device is suitably used as a bearing device for a spindle motor in a magnetic disk drive like an HDD, an optical disk drive for a CD-ROM, CD-R/RW, DVD-ROM/RAM, or the like, or a magneto-optical disk drive for an MD, MO, or the like, or as a bearing device for a motor such as a polygon scanner motor of a laser beam printer (LBP), a color wheel motor of a projector, or a fan motor.
Normally, in a fluid dynamic bearing device, a shaft portion of a shaft member is inserted along an inner periphery of a bearing sleeve or the like, and a radial bearing portion is constituted between the outer peripheral surface of the shaft portion and the inner peripheral surface of the bearing sleeve. Further, in some fluid dynamic bearing devices, a flange portion is provided at one end of the shaft portion, and between the end surface of the flange portion and the surface opposed thereto (for example, the end surface of the bearing sleeve), a thrust bearing portion is constituted (for example, refer to Japanese Patent Application Laid-open No. 2003-239951).
As described above, the outer peripheral surface of the shaft portion constitutes a radial bearing portion, and the end surface of the flange portion constitutes the thrust bearing portion. Thus, it is necessary to finish those surfaces with high accuracy. Simultaneously, in the case where the radial bearing portion and thrust bearing portion are constituted together with each other, it is important to take into consideration not only the surface accuracy of the individual bearing portions, but also the shape accuracy therebetween, that is, perpendicularity between the outer peripheral surface of the shaft portion and the end surface of the flange portion.
Proposed examples of a method of integrating the shaft portion and the flange portion separated from each other with high accuracy include fixation means in which an annular thrust plate is press-fitted to a fixation shaft (for example, refer to Japanese Patent Application Laid-open No. 2000-324753 and Japanese Patent Application Laid-open No. 2001-317545).
Further, as another means for fixing the shaft portion and the flange portion by press-fitting with high accuracy, there has been proposed a press-fitting device in which a guide member is used and press-fit fixation is performed with use of a shaft member (shaft portion) which is provided with an R portion on the outer periphery of the lower end thereof and a ring member (flange portion) which is provided with a chamfered portion on the inner peripheral edge of the upper end of the hole thereof, the guide member having a shaft holding surface and a ring contact surface which are worked so as to achieve perpendicularity of high accuracy therebetween, the R portion and the chamfered portion are brought into contact with each other at the time of starting press-fitting (for example, refer to Japanese Patent Application Laid-open No. 2001-287124). In this case, first, the R portion provided at the lower end of the shaft member is brought into contact with the chamfered portion of the hole of the ring member. With this operation, the ring member is moved in the horizontal direction, whereby press-fitting is performed in the state in which the shaft member and the ring member are coaxial with each other.
Further, in accordance with recent downsizing and enhancement in portability of information devices, there has been demanded enhancement in resistance to falling-off and the like (impact resistance) with respect to fluid dynamic bearing devices mounted to those information devices. Accordingly, when the shaft member is constituted by the shaft portion and the flange portion separated from each other, it is important to increase fastening strength therebetween.
As means for increasing the fastening strength, there has been proposed, for example, means by which a flange portion is pressurized in the axial direction in a seal state in which an expansion of an outer diameter portion of a flange material is regulated, and the inner peripheral surface of the flange portion is reduced in diameter, whereby fastening fixation with respect to the shaft portion is achieved (for example, refer to Japanese Patent Application Laid-open No. 2004-204916).    [Patent Document 1] Japanese Patent Application Laid-open No. 2003-239951    [Patent Document 2] Japanese Patent Application Laid-open No. 2000-324753    [Patent Document 3] Japanese Patent Application Laid-open No.    [Patent Document 4] Japanese Patent Application Laid-open No. 2001-287124    [Patent Document 5] Japanese Patent Application Laid-open No. 2004-204916